noaa atlas 14 volume 11 · dongjin seo –university of texas at arlington steve fitzgerald...

NOAA ATLAS 14 – VOLUME 11

February 27th, 2019CRS Users Group MeetingMikaela Mahoney, Hydraulic EngineerU.S. Army Corps of EngineersFort Worth District

NOAA ATLAS 14 METEOROLOGY RESEARCH INCENTIVE

▪ What is it:▪ Precipitation frequency estimates

▪ How much rain in a 100-year storm event

▪ Non-regulatory

▪ Benefits:▪ Better understanding of the risk from extreme

precipitation events

▪ Infrastructure design – parking lots to dams

▪ Floodplain mapping (NFIP), where can we safely construct new neighborhoods

▪ Preparedness or mitigation planning

▪ Schedule: Complete▪ Volume 11 (Texas) released September 2018

▪ Documentation published January 2019

▪ Further studies in the works with NOAA

NOAA Atlas 14

2

PREVIOUS PRECIPITATION FREQUENCY PRODUCTS

3

NOAA/NWS USGS

▪ NWS Technical Paper No. 40 (1961)

▪ NWS Technical Paper No. 49 (1964)

▪ NWS Hydro-35 (1977)

▪ Atlas of Depth-Duration Frequency of

Precipitation Annual Maxima for Texas (2004)

TP40: 100-yr 24hr USGS: 100-yr 24hr

IMPORTANCE OF NEW DATA

4

▪ Hydro-35/TP 40 - ~20-years of record

▪ USGS - ~35-years of record

▪ NA14 - ~60-years of record

NUTS AND BOLTS OF NOAA ATLAS 14

5

▪ Data Collection

▪ Gathered data from 11,930 stations; retained

3,900 stations

▪ Extracted AMS from each station

▪ Regionalization Approach

▪ Trading space for time

▪ Results on more accurate estimates of extreme

quantiles

▪ Frequency Analysis

▪ Fit multiple distributions to identify best fit for

each station and duration

▪ Ultimately used GEV probability distribution

Approach: Regional frequency analysis approach based on L–moment statistics calculated from annual

maximum series (AMS)

1990 1991 1992 1993 1994 1995 1996 1997 1998 19990

1

2

3

4

5

6

Daily p

recip

itation (

in)

1990 1991 1992 1993 1994 1995 1996 1997 1998 19990

1

2

3

4

5

6

Year

Daily p

recip

itation (

in)

Source: NOAA Atlas 14 Volume 11 Version 2

NUTS AND BOLTS OF NOAA ATLAS 14

6

▪ Uncertainty Bounds

▪ Utilized a Monte-Carlo approach to estimate 90%

confidence bounds

▪ Simulated 1,000 data sets for each station and

duration

▪ Precipitation Grids

▪ Accounts for variations in terrain, coastal

proximity, mean annual precipitation, and

distance from station


PRECIPITATION DATA

7

▪ Digitized pre-1948 data from NCEI’s

Climate Database Modernization Program▪ Data screened for quality

▪ Merged nearby stations (within 3–5 miles, ~same

elevation)

▪ Length of record (>30 years of data)

▪ Extracted AMS for durations between 15-min and 60-

day from precipitation records across the state

▪ Average record length ~60 years

▪ Records extended through December

2017, where available ▪ A few stations included data through June 2018

Stations recording at 1-Day Intervals


REGIONALIZATION

8

▪ Initial region for each station consisted of

closest 15 gages

▪ Included highest 1-hour or 1-day peak

within 60 miles

▪ Refinement of regional gages based on:

▪ Distance from target station

▪ Topography

▪ Mean annual maxima

▪ Maximum recorded values

▪ Record lengths

▪ Analyzed L-moment statistics for each gage

within the region

▪ Typical density: 15-25 gages, 700-1,800

data years (daily record)


FREQUENCY ANALYSIS

9

▪ Multiple probability distributions fit to each station and duration

▪ GEV distribution chosen for all durations based on multiple goodness of fit tests

▪ Kolmogorov-Smirnov and Χ2 Test

▪ Precipitation frequency estimates based on regional L-moments from each station

▪ Some smoothing required

Original Estimates

Adjusted Estimates


HURRICANE HARVEY

10

▪ Broke all multi-day rainfall

records

▪ Official highest amount of

rainfall ever to fall on the

continental U.S.

▪ Harvey affected results of 2-

day through 20-day estimates

for 1000-year event

▪ No significant skew for the

1000-year 24-hour or 1000-

year 30-day results

Original Estimates

Adjusted Estimates


UNCERTAINTY BOUNDS

11

▪ Monte Carlo simulation accounts for inter-station dependencies

▪ 1,000 simulations simulated for each station

▪ Accounts for natural variability (uncertainty in parameters) but not knowledge uncertainty

(selected distribution)


GEOSPATIAL MAPPING

12

▪ Interpolated based on mean annual maxima

and 2-year spatial pattern using a hybrid

statistical-geographical approach developed

by PRISM (Oregon State University)

▪ Multiple iterations were made to insure

satisfactory spatial patterns and peer review

comments

▪ Bulls eyes, geographic features, logical distribution

of precipitation Version 1

Version 2

NOAA ATLAS 14 – PEER REVIEW BOARD

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▪ Dr. John Nielsen-Gammon – Texas A&M

University/State Climatologist

▪ Dr. William Asquith – Texas Tech University/USGS

▪ Dr. Nick Fang – University of Texas at Arlington

▪ Dr. Dongjin Seo – University of Texas at Arlington

▪ Steve Fitzgerald – Harris County Flood Control

District

▪ Daniel Huckaby – NWS

▪ Paul McKee – NWS

▪ Maureen O’Leary – NWS

▪ Jon Zeitler - NWS

▪ Jason Johnson – NWS

▪ Alan Johnson – FEMA

▪ Saul Nuccitelli - TxDOT

▪ Simeon Benson – USACE

▪ Jerry Cotter - USACE

▪ Craig Loftin – USACE

▪ Helena Mosser – USACE

▪ Steve Pilney – USACE

▪ Max Strickler – USACE

NOAA ATLAS 14 - ACCESS

14

▪ All data and resources located on the Precipitation Frequency Data Server (PFDS)

▪ http://hdsc.nws.noaa.gov/hdsc/pfds/

http://hdsc.nws.noaa.gov/hdsc/pfds/

RESULTS

15

COMPARISON TO PREVIOUS STUDIES

16

NA 14 – TP40

100-yr 24-hr

NA 14

100-yr 24-hr

COMPARISON TO PREVIOUS STUDIES17

NA 14

100-yr 24-hr

NA 14 – USGS

100-yr 24-hr

Up to 30% increase for 100-year

24-hour precipitation from USGS

NORTH CENTRAL TEXAS PRECIPITATION FREQUENCY DIFFERENCES

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▪ Between 5% decrease and 2% increase in precipitation in North Central Texas

8

8.5

9

9.5

10

10.5

11

Parker County Tarrant County Dallas County Ellis County Denton County Kaufman County Hunt County

Differences in Precipitation Frequency Estimates100-yr 24-hr

Atlas 14 USGS TP-40

WE HAVE NOAA ATLAS 14, ARE WE DONE YET?

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▪ Areas of concern

▪ Short period of observations

▪ Relationship between extreme weather

variability and climate change/climate variability

▪ Evaluation of non-stationarity with respect to

estimates

▪ NA 14 are point estimates

▪ Need to update Area Reduction Factors (ARF)

▪ Need for additional studies ($3 - $4M)

▪ Other methods to estimate precipitation

frequency Trend analysis

▪ Storm studies (design storms)

▪ Atlas 14 Upkeep

▪ Who will update in 10-20 years?

▪ How will it be funded?

NOAA ATLAS 14 IMPACTS

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▪ More accurate estimates spatially → better

preparedness and response

▪ Able to better quantify the degree or risk of

flooding at a location

▪ New delineation of floodplain maps

▪ Frequency of precipitation does not equate to

frequency of flooding

▪ Better planning/design of infrastructure

▪ More resilient towards future storms

▪ Non-Regulatory

▪ No current requirement for communities or

agencies to use Atlas 14 values

QUESTIONS?

21

Mikaela Mahoney

[email protected]

817-886-1546

mailto:[email protected]

WHAT IS NOAA ATLAS 14?

22

▪ NOAA’s Office of Water Prediction, Hydro-

meteorological Design Studies Center

▪ National initiative which begun around 2000

▪ Today’s de facto national standard for

precipitation frequency estimates

▪ 30 arc-second resolution, ~800 meter grid ▪ Durations from 5 minutes to 60 days for

▪ Average recurrence intervals (ARIs) from 1 to 1,000

years

▪ Electronically accessible ▪ http://hdsc.nws.noaa.gov/hdsc/pfds/

▪ Funded locally

http://hdsc.nws.noaa.gov/hdsc/pfds/

INFRM – NOAA ATLAS 14 PEER REVIEW BOARD

File Name

23

▪ Appropriateness of selected

distribution

▪ How many data points equaled or

exceeded estimate

▪ Variability of estimates over time

TREND ANALYSIS

24

Spatial results of t-, Mann-Kendal, and Levene’s test for 1-day AMS.


No Trend

Positive Trend

Negative Trend

Change in Variance


25

NA 14

100-yr 6-hr

NA 14 – USGS

100-yr 6-hr


26

NA 14 – USGS

100-yr 1-hr

NA 14

100-yr 1-hr

NOAA ATLAS 14 – VOLUME 11

27

▪ Updated precipitation frequency estimates

for Texas

▪ Quantify the degree or risk of flooding at a

location

▪ Improved statistical techniques with longer

record lengths – more reliable estimates

▪ Easily accessible

▪ Not done yet, still need more research

▪ Area Reduction Factor

▪ Non-stationarity of data

▪ Climate change

Atlas 14City of Austin Outreach

Efforts

Communicating risk, educating the public, and engaging the development community.

City of Austin Watershed Protection DepartmentNorth Texas Floodplain Administrators Group | February 27, 2019

Overview

• Study background

• Summary of key impacts

• Recommended response

• Next steps

2

Measure Current Updated Percent Increase

100-year rainfall 10.2 inchesUp to 13+

inches30%

Key impacts of Atlas 14 updated rainfall data

*Excludes Colorado River floodplain and associated lakes

3



inches30%



inches30%

Buildings in 100-

year floodplain4,000 7,200* 80%

Floodplains Will Expand• More homes and businesses are at risk

of flooding than previously thought.

• Affects ability to develop, remodel, or redevelop property.

• Affects the need for and the cost of flood insurance.

• Floodplains will need to be re-studied.

• See impacts at ATXfloodpro.com

Austin’s

Floodplains Will ExpandAustin’s

• More homes and businesses are at risk of flooding than previously thought.

• Affects ability to develop, remodel, or redevelop property.

• Affects the need for and the cost of flood insurance.

• Floodplains will need to be re-studied.

• See impacts at ATXfloodpro.com

Impact to Flood Insurance?• Flood insurance impacts are

dependent on FEMA map update

• Map updates at least 3 years away

• Rates may go up

• Insurance requirements may change

• Talk to an insurance agent now

What is the

Proposed Floodplain Regulations

Recommended Response

Step 1

Land Development Code amendments

Step 2

Drainage Criteria Manual revisions

Step 3

Floodplain Study and Mapping Updates

Floodplain Management Regulation Changes

• Redevelopment Exception

• Colorado River Exception

• Freeboard

Step 1: Land Development Code Amendments

Proposed Interim Floodplain Definitions

Storm Level

Current Rainfall

Depth

(24 hour storm)

Updated

Rainfall Depth

(24 hour storm)

100-year

(1% chance)10.2 inches

Up to 13+

inches

New 100-yr

floodplain

Current 500-yr

floodplain ==>>

New 25-yr

floodplain

Current 100-yr

floodplain ==>>

Step 1: Land Development Code Amendments

Storm Level

Current Rainfall

Depth

(24 hour storm)

Updated

Rainfall Depth

(24 hour storm)

100-year


Up to 13+

inches

500-year

(0.2% chance)13.5 inches

Up to 19.5

inches

Storm Level

Current Rainfall

Depth

(24 hour storm)

Updated

Rainfall Depth

(24 hour storm)

25-year


Almost 10

inches

100-year


Up to 13+

inches

500-year

(0.2% chance)13.5 inches

Up to 19.5

inches

Redevelopment Exception

A residential building may encroach in the 25- or

100-year floodplain as long as it:

• Replaces an existing building

• Is above 100-year floodplain by 2 feet

• Does not increase number of dwelling units

• No adverse flooding impact

If these conditions are met, safe access

requirement is waived.

Redevelopment ExceptionRemodels

Additions and substantial renovations can

be approved if:

• The home meets 2 feet freeboard

requirement.

Colorado River Exception

• Expand 100-year encroachment exception to include Lake Austin and Lake Travis

• Maintain prohibition on encroachment on 25-year floodplain

Lake

Travis

Lake

Austin

Lady Bird

Lake

Colorado River

downstream of

Longhorn Dam

Increase Minimum freeboard to 2 feet

• Minimum height between building’s lowest floor and 100-year floodplain

• Freeboard is the single-most effective means for reducing flood risk to a building in the floodplain

• More than 140 Texas communities have freeboard of 2 feet or higher

Helpful Documents to View

• Guidance document

o Long-term planning recommendations regarding the proposed floodplain

regulations and drainage rules

• Summary of recommended code changes

o Draft ordinance explanation in non-legislative language

• Draft ordinance

o Proposed changes to the Land Development Code in legislative format

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Step 2: Drainage Criteria Manual Revisions

• DCM updates are related to but independent from floodplain code amendments

• Potential changes include:

• Design rainfall depths

• Rainfall temporal distribution (hyetograph)

• Intensity-duration-frequency curves

• Additional Considerations

• Impact on storm drain and detention pond sizing

• Level of service requirements

Key Changes

• Higher Rainfall Depths across

all depths and durations

• Increased geographic variability

17

Percent increase indicated by Atlas 14 versus current DCM

18

2 5 10 25 50 100 250/200 500

5 min* 9% 8% 11% 14% 17% 18% 17% 21%

15 min 8% 7% 8% 10% 10% 10% 5% 7%

30 min 12% 10% 12% 14% 15% 14% 11% 15%

1-hr 13% 9% 10% 11% 10% 9% 4% 7%

2-hr 11% 8% 10% 13% 14% 14% 11% 15%

3-hr 14% 11% 14% 18% 20% 22% 20% 25%

6-hr 16% 15% 19% 24% 27% 30% 29% 34%

12-hr 16% 16% 20% 25% 27% 30% 28% 33%

24-hr 17% 9% 11% 14% 16% 20% 21% 28%

Recurrence Interval (year)

Key Changes

• Increased geographic

variability

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Geographic variation: Percent difference indicated by Atlas 14

Manchaca (South) versus Round Rock (North)

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1 2 5 10 25 50 100 200 500 1000

5-min: 0.00 0.02 0.04 0.05 0.06 0.04 0.05 0.06 0.07 0.08

10-min: 0.00 0.02 0.04 0.05 0.05 0.06 0.05 0.06 0.06 0.08

15-min: 0.00 0.02 0.04 0.05 0.06 0.05 0.05 0.06 0.07 0.08

30-min: 0.01 0.02 0.05 0.06 0.06 0.06 0.05 0.06 0.07 0.09

60-min: 0.01 0.03 0.05 0.06 0.07 0.06 0.06 0.07 0.08 0.10

2-hr: 0.03 0.04 0.06 0.06 0.07 0.08 0.08 0.09 0.10 0.11

3-hr: 0.02 0.04 0.06 0.06 0.08 0.08 0.09 0.10 0.12 0.13

6-hr: 0.03 0.05 0.06 0.07 0.08 0.09 0.11 0.11 0.13 0.14

12-hr: 0.03 0.05 0.06 0.07 0.09 0.10 0.12 0.13 0.14 0.14

24-hr: 0.02 0.04 0.06 0.07 0.09 0.10 0.12 0.13 0.14 0.15

2-day: 0.00 0.03 0.05 0.07 0.09 0.11 0.12 0.13 0.15 0.16

3-day: 0.00 0.03 0.05 0.07 0.09 0.11 0.12 0.13 0.15 0.16

4-day: -0.01 0.03 0.05 0.06 0.08 0.10 0.13 0.14 0.15 0.16

7-day: -0.01 0.02 0.04 0.06 0.09 0.10 0.12 0.14 0.15 0.16

10-day: -0.01 0.02 0.04 0.06 0.08 0.09 0.11 0.13 0.15 0.16

20-day: -0.02 0.01 0.03 0.05 0.07 0.08 0.10 0.12 0.13 0.15

30-day: -0.02 0.01 0.02 0.04 0.06 0.07 0.09 0.11 0.13 0.14

45-day: -0.01 0.01 0.03 0.04 0.06 0.07 0.08 0.09 0.12 0.13

60-day: -0.01 0.01 0.02 0.04 0.05 0.07 0.08 0.09 0.10 0.11

Evaluate various approaches to

capturing the spatial variability of

extreme rainfall

• Single value

• Major Watersheds

• North/South

• By County

• Something Else

21

IDF Curves

Fit the depth values to a

power function to obtain a

continuous curve

TxDOT format:

Intensity (in/hr) = a/(t+b)c

22

i = 102.6/(t+12)0.77

Time Distribution Issues

• NRCS Type III

• HEC-HMS Frequency Storm

• An invariant nested Scheme

23

• 2019 to 2021 – Re-mapping of Austin floodplains

• Approximately 1200 stream miles

• HEC-RAS 2D modeling in selected areas

• Coordination with other impacted communities

• 2022 to 202? – FEMA map updates

• Letters of Map Revision

• Physical Map Revision

Step 3: Floodplain Study and Mapping Updates

Outreach

Atlas 14 Web Pages

Coming Attractions

• Frequently Asked

Questions Page

• Presentation video with

Spanish narration

• Draft code language

• Dates for Boards and

Commission meetings

• Dates for Council meeting

FloodPro

Who We Have Talked To

Presentations to over 1,200 people from 40 different groups

Stakeholder Meetings

• Two internal stakeholder meetings

• Two external stakeholder meetings

General Public meetings (5)

• Determined location by most impacted areas

• Two meetings regarding floodwalls (Districts 1 and 2)

Webinar access provided for external stakeholder and public meetings

• Presentations and Webinar files available on City website

Outreach through social media

24,000 postcards sent to residents in the floodplain 28

Postcards (100-year, 500-year, Meeting Notices)


Presentations to over 1,200 people from over 40 different groups

Professional Associations

• ASCE, ACEA, AIA, ABoR, NAPMW, TWRN, SMPS

Development Organizations

• RECA, HBA, DAA, WCC, SCC, AIC

Neighborhood groups

• ANC, OCHOA, SCNPCT

Boards and Commissions

• COJC, EC, ZAP

Individual Engineering, Real Estate, and Title Company Representatives

30

Presentations to over 1,200 people from 40 different

groups

Internal Departments

• Development Services Department

• COA Director’s meeting

• Parks and Recreation Department

• Capital Planning Office

• Law

• Public Works Department

Council Offices

• Districts 1, 2, 6, 10


31

• Austin Transportation

Department

• Austin Water Utility

• Neighborhood Housing and

Community Development

• Sustainability Office

• Office of Real Estate Services

• Aviation Department

Coordination with Travis County

• Parallel updates to Title 30 of the Land Development Code

• July 31, 2018 – Initial presentation to Commissioners Court

• November 13, 2018 – Commissioners Court voted to approve $22 million increase in 2017 bond program

• January 2019 – Public hearing to consider Atlas 14 changes to Title 30

Coordination with Other Communities

Regional Coordination

• Series of meetings with Central Texas counties and communities

• Hosted by TxDOT

North Austin Metro Area

• Williamson County

• Upper Brushy Creek WCID

• Other cities

Issue Ramification Resolution

Hot Button Issues

Subchapter F (McMansion) compliance Higher floodplain and freeboard have impacts on maximum height

No change recommended; Analysis shows minimal impact

Visitability Compliance Higher floodplain and freeboard have impacts on accessibility

No change recommended; Existing code offers way to comply

Maximum home size in redevelopment exception

Limits desired home size Removed from exception requirement

Ordinance approval timeline too fast Impacts development in progress Extended timeline and outreach efforts

Permitting uncertainty for long-term planning and multi-phase developments

Uncertainty increases development costs Providing floodplain recs. since July; drainage design recs. by December

No commercial use allowed to use redevelopment exception

No incentive for commercial properties to reduce flood risk

Will consider during FP restudy periodrecs. by December

Environmental buffer zone enlargement Less developable area No change recommended; Small area impacted

Environmental Resources Inventory required more often

Increased Development Costs Revise ECM to eliminate requirement of ERI outside of buffer zone

Parkland dedication impacts Floodplain area discounted toward required area dedicated

No change recommended; Relatively small area impacted

No floodplain disclosure for tenants Residents not aware of flood risk Will consider during FP study period

Follow our progress

AustinTexas.gov/atlas14

Contact us

[email protected] Hotline 512-974-2843

View floodplains

ATXfloodpro.com